Historically, crab and lobster fishermen have used two ropes joined together by a knot and attached one end to a float and the other end to a trap or "pot" employed for deep water fishing.
A normal rigging employs a sinking line having a specific gravity greater than one, i.e. a specific gravity greater than that of water, which extends from the float and having a length typically on the order of twenty-two (22) fathoms. The sinking line prevents the rope from floating upon the surface, thereby creating a potential hazard. At this point, the sinking line is joined, i.e. knotted to, a floating line having a specific gravity less than one with the length of the floating line being determined by the depth of the water. The floating line is then joined to the "pot". This design is extremely advantageous for use in such deep sea fishing since fishermen desire that the line attached to the "pot" should not scare the catch. This objective is accomplished by the floating rope section which floats above the "pot".
Joining the floating and sinking rope sections with a knot is disadvantageous since a knot of any type reduces the strength of a line by 50 percent. The knowledge of this degradation in strength has lead to the development of a partially leaded polypropylene line having a lead wire incorporated into a portion of the rope, said lead wire extending over a length of the order of twenty-two fathoms. A sufficient amount of lead is used to overcome the specific gravity of polypropylene which is less than that of water. In producing the rope, when the length of twenty-two fathoms is reached, the lead wire is terminated and the remainder of the rope length is formed by continuing the polypropylene portion of the rope which, having a specific gravity less than water (i.e., less than 1.0), floats.
Although the last-mentioned design provides a floating/sinking rope yielding the desired objectives of the fishermen, there are nevertheless some important deficiencies which include the following:
1. In cold water the ductility of the lead is significantly reduced and the lead becomes brittle. Due to the natural elongation of the polypropylene line when in use (the elongation is commonly of the order of 15 percent) the lead breaks, and, through continued use, the lead works its way out of the line thereby decreasing its sinkability.
2. The lead lost into the sea becomes an environmental threat, due to its toxicity (i.e., lead is poisonous).
3. The polypropylene line softens due to the voids caused by the lead which has worked its way out of the polypropylene line causing the line to wear more quickly thus significantly reducing its operating life.
4. The lay of the entire line changes as the rope, when floating freely, works itself toward a neutral lay or degree of twist.
It is, therefore, extremely advantageous to provide a rope having all the characteristics of the floating/sinking ropes of the prior art which overcome the disadvantages of lead filled rope and rope whose floating and sinking portions are knotted together.